Steel cross ties have been used for over a century in railways throughout the world. Like timber cross ties there has been little need to make any major modifications to their design, such that existing designs for steel cross ties and their related elements no longer meet present-day track requirements.
Until 1920, when creosoted wood ties became available, steel ties were used extensively, and both the beam and channel types were produced. As the life of the untreated wood tie was increased from approximately 8 years to approximately 30 years, by the creosoting treatment, steel ties became noncompetitive. However, small quantities of steel ties have been produced recently for light duty service in mines and foreign narrow gage railroads.
The relatively low recent usage of steel cross ties throughout the world has been attributed to both technical and economic considerations. The difficulties of maintenance, particularly packing and alignment, were real before the introduction of mechanical tampers, but at present it is felt that these difficulties are unreal and the strong evidence of overseas employment of the same must be taken into account. Prompted by the continually increasing prices and reduced availability of good hardwood railroad cross ties, several railroads within the United States have made serious studies regarding the possible availability of a suitable steel tie that is priced competitively.
In view of the high price of wood ties, the reduced availability of better grades of hardwood, and the reluctance of the railroads to use concrete ties, there has been a definite promotion of development of a steel cross tie. Moreover, the increased labor costs for maintaining wooden ties, in addition to increased tie plate wearing due to newer and larger freight cars, has necessitated a reevaluation of the steel tie with regard to currently operating as well as future planned railroads.
The first metal cross tie was made from cast iron and was used in Scottish mines at the beginning of the 19th century in the form of flat plates. The trough-type cross tie appeared in England about 1860 and spread to France, Germany and Switzerland about 1870. They did not spread any further in Europe because of local timbers, while their use in England was limited because of corrosion problems.
Many fastening systems were possible as the thin plate of the early steel tie made bolting an easy task. Unfortunately, some bolting systems became very complicated, particularly where different sizes of rail and change in gages was attempted. Loss and identification problems regarding the components of a bolted fastening system have resulted in unnecessary expense that has led to the lack of popularity in the steel cross tie.
Information relating to the performance of steel ties indicates several deficiences which must be corrected if a satisfactory tie is to be developed. Steel ties have a tendency to move in the ballast in the direction of train travel and become bunched even though properly spaced and ballasted originally. This occurs either because the retaining clips have inadequate holding power or because the ballast was not properly interlocking with the tie.
Based upon information obtained from both current and previous considerations, the following performance prerequisites must be considered if an acceptable steel tie is to be developed. First, the steel tie must resist bending moments (positive under the rails and negative at the center) in a manner similar to the present hardwood cross tie. Secondly, the steel cross tie must restrain track movements both in the lateral and longitudinal direction by interlocking with the ballast. Thirdly, the rails must be anchored securely to the cross tie (using rail anchors) to resist longitudinal movement. This is especially true for those situations in which welded rai is used. Fourth, unless the horizontal bearing surface of the tie is increased, present tie spacing on 24 inch centers for yard track and 22 inch centers for main line track must be maintained because the support of power of the present ballast and subgrade construction is at the allowable maximum for 100 ton cars.
One additional problem which must be solved relates to electrical insulation of the rail from the tie and other related equipment. Provision must be made for electrical insulation of the ties used in main line track from the rails so that existing traffic control and signaling systems can be used. In particular, switching and traffic control signals are currently sent through at least one of the rails on the track for controlling railroad traffic along the main line of a railway. With wood ties, this does not become a problem as the rail is automatically insulated from the tie by its inherent design. Insulation of the rails for track circuitry has been achieved by durable pads between the rail and the steel tie. Currently employed systems, however, do not fully insulate the rail from the other associated equipment or are not applicable to welded rail in which rail anchors must be used to prevent longitudinal movement of the rail. Moreover, any contemplated systems use a plethora of elements for achieving a singular insulative result and, as such, are cumbersome, expensive and easily lost.